Optical communication links have to employ polarization multiplexing and coherent modulation & detection for increasing data rates in optical transport systems. Coherent links carrying more than 100-Gbps over single optical carrier have been demonstrated till date. Typically, receivers for coherent, polarization multiplexed transmission systems use ultra-fast ADCs (analog-to-digital converters) that convert electrical signals to the digital domain. These signals are then jointly processed using digital signal processors (DSPs) to recover the transmitted data.
In prior art, digitization of such high-speed signals is extremely difficult. Once the digitization is done, processing of these signals is also very challenging, since massive amount of computation is required to meet the extremely high throughput rates for real-time operation. Digitization of the signals obtained at the receivers of high-speed coherent optical links is extremely difficult because of the large bandwidth required for this purpose. High-speed ADCs add significant overheads in terms of power consumption, design complexity, chip area and cost.
In the view of the foregoing, there is a need for a receiver for processing data signals in coherent transmission system, in analog domain itself, without first converting them to digital domain using high-speed ADCs.